The present invention relates to radiation deflectors and radiation deflector assemblies and in particular to radiation deflectors and assemblies of the kind described in U.S. Pat. No. 4,854,658, issued Aug. 8, 1989 in the name of the present applicants. Commonly assigned U.S. Pat. Nos. 4,871,244 and 4,867,532 also show similar apparatus and methods for deflecting optical beams and selecting wavelengths of radiation.
Radiation deflector assemblies described in U.S. Pat. No. 4,854,648 comprise at least three radiation waveguides; a controllable radiation deflector positioned such that when the deflector is in a first position radiation passes between one combination of two of the waveguides, and when the deflector is in a second position radiation passes between another combination of two of the waveguides; and control means responsive to control signals for controlling the position of the deflector. In the specific embodiment described in U.S. Pat. No. 4,854,648 the deflector comprises a cantilever beam mounted and hinged in a common substrate with the waveguides. This configuration of radiation deflector assembly hereinafter referred to as "of the kind described" eases the problem of accurately aligning the waveguides with the deflector.
Radiation deflector assemblies of the kind described find application as radiation switches; for example, as optical switches in optical transmission systems.
One problem with the construction of radiation deflector assemblies of the kind described is the need to make the radiation deflector attain equilibrium as rapidly as possible on switching, without excessive resonant oscillation. The deflector must also have a minimum displacement sufficient to deflect radiation by a distance at least equal to the separation between each of the waveguides in respective waveguide pairs.
It is further desirable that where the control means requires a driving potential to control deflection of the deflector, this driving potential is minimised.
It is an object of the present invention to provide improved radiation deflectors and deflector assemblies of the kind described which resolve or at least partially mitigate one or more of these aforementioned problems.
According to the present invention a radiation deflector comprises a deflectable cantilever beam of which one end is free and one end is hinged to a supporting substrate wherein the cantilever beam has its centre of mass closer to the free end of the beam than to the hinged end.
Also according to the present invention a radiation deflector assembly of the kind described comprising a deflectable cantilever beam of which one end is free and one end is hinged to a supporting substrate is characterised in that the cantilever beam has its centre of mass closer to the free end of the beam than to the hinged end.
Conveniently, the cantilever beam comprises a beam portion hinged to the substrate and a load portion at the free end of the beam portion. Preferably the load portion provides the major proportion of the total mass of the cantilever beam as a whole, the centre of mass of the load portion being arranged to be positioned at or near the free end of the beam portion.
It has been found that a cantilever beam radiation deflector according to the present invention facilitates the more rapid attainment of equilibrium on switching.
Preferably the length of the beam portion and the mass of the load portion are selected such that the first natural resonant frequency of the cantilever beam is much greater than the maximum frequency at which the deflector is to be switched between positions.
Conveniently, in a radiation deflector assembly according to the invention, the control means comprises means for applying an electrostatic potential for displacing the cantilever beam deflector. The control means may include an electrode arranged such that the displacement force provided by an applied electrostatic potential effectively acts at the centre of mass of the load portion.
Conveniently, the electrostatic potential may be applied to a side surface, being a surface of the load portion substantially parallel to the longitudinal axis of the undisplaced beam portion. Preferably the area of the side surface is made relatively great in order to reduce the electrostatic potential required to provide the necessary displacement force.